### Author Topic: Roof Drains  (Read 5575 times)

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#### Russ

• Guest
##### Roof Drains
« on: March 04, 2005, 09:13:29 AM »
I'm working on the roof plans for a Hotel and can't remember the formula for figuring how many drain pipes I need per square foot of surface area.

#### JohnK

• Seagull
• Posts: 10626
##### Roof Drains
« Reply #1 on: March 04, 2005, 09:19:25 AM »
There's a formula for that?!?!

...Ive been doing it the long way. Calculating the rainfall, and basing the locations and size on the slope of the roof and pipe, the area its serving (-ie in a wide open roof, or located next to a wall...etc.)
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#### ronjonp

• Needs a day job
• Posts: 7527
##### Roof Drains
« Reply #2 on: March 04, 2005, 10:08:40 AM »

Windows 11 x64 - AutoCAD /C3D 2023

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#### rktect3j

• Guest
##### Roof Drains
« Reply #3 on: March 04, 2005, 10:57:16 AM »

#### Dent Cermak

• Guest
##### Roof Drains
« Reply #4 on: March 04, 2005, 11:12:57 AM »
One at each corner ??

#### glee

• Guest
##### Re: Roof Drains
« Reply #5 on: October 11, 2005, 06:54:54 PM »
Another thing to have in the back of your mind is once you figure out the minimum number of roof drains, you should factor in the built up roof slopes you have.  That is the built up roofing that gets you your drainage back to the roof drains and overflow (if you are required to have an overflow).
1/4" in 12" actually is a difficult minimum slope to achieve for some contractors.  3/8" in 12" being a better minimum except where the roof area being too large that by the time you are done, you have built up roofing 12" or more deep.  If that's ok with you, fine.  Otherwise you may want to add more drains to have smaller backslopes.
Umm, not sure if what I wrote above makes sense.  But you'll figure it out.  Sometimes it's a good idea to go above your minimums number of roof drains.  Especially on hotel roofs where you may have so much mechanical/ kitchen eqpt. & whatnot that all that built up roofing, gets in the way.